In a small engine-driven working machine, since an engine may be disposed adjacent to an operator or a high temperature exhaust gas may be discharged from a muffler, various attempts have been made to install a muffler cover to prevent the operator from coming in direct contact with a muffler or decrease the temperature of an exhaust gas discharged outside of the muffler cover. For example, in Patent Literature 1, an exhaust gas temperature is decreased by introducing cooling air generated by a cooling fan into a muffler chamber and mixing an exhaust gas with the cooling air in a cover.